1. Field of the Invention
The present invention relates to an electrooptical device having driver circuits consisting of semiconductor devices making use of thin-film semiconductors and also to a method of fabricating such an electrooptical device. More particularly, the invention relates to an active matrix electrooptical device (AMEOD) where a pixel matrix circuit and logic circuitry are integrated on the same panel.
2. Description of the Related Art
In recent years, techniques for fabricating thin-film transistors (TFTs) on an inexpensive substrate have evolved rapidly, because there is an increasing demand for active matrix electrooptical devices. In an active matrix electrooptical device, millions of pixels are arranged in rows and columns. TFTs are arranged at each pixel. Electric charge going into and out of each pixel electrode is controlled by the switching action of each TFT.
Electrooptical devices include liquid crystal displays making use of optical characteristics of liquid crystals, electroluminescent displays employing electroluminescent materials typified by ZnS:Mn, and electrochromic displays exploiting the color changing characteristics of electrochromic materials.
These electrooptical devices are active devices that can be matrix-addressed. High-definition display can be accomplished by utilizing this active matrix construction. As mentioned above, a great feature of the active matrix construction lies in that electric charge going into and out of pixel electrodes arranged in rows and columns within an image display region of an electrooptical device is controlled by turning on and off pixel electrodes disposed at the pixels.
Another feature of the active matrix construction is that driver circuits for driving pixel TFTs are necessary to control pixels. In the prior art technique, a pixel matrix circuit formed on a glass substrate has been connected with a separately prepared driver IC to form an active matrix circuit.
In recent years, however, it has become common practice to form plural circuit TFTs forming driver circuits and a pixel matrix circuit on the same substrate to build driver circuits (known as peripheral driver circuits) around the pixel matrix circuit.
More recently, a system-on-panel (SOP) structure has attracted attention comprising a substrate on which control circuits (e.g., a processor circuit, memory circuits, A/D or D/A converter circuits, correcting circuits, and a pulse-generating circuit) are formed, as well as driver circuits (such as shift register circuits or buffer circuits) for driving pixel TFTs.
A general construction of an electrooptical device is shown in FIG. 3, which gives an example of active matrix liquid crystal display. A pixel matrix circuit 302 is formed on a glass substrate 301. This pixel matrix circuit 302 consists of integrated pixel regions. A portion of the pixel matrix circuit 302 is shown on an expanded scale at 303, where plural regions (two regions in this example) are arranged in rows and columns. At least one pair of pixel TFT/pixel electrode is disposed in each pixel region.
A horizontal scanning driver circuit 304 for transmitting data signals to data lines comprises shift register circuits, level-shifting circuits, buffer circuits, and sampling circuits. The level-shifting circuits amplify driving voltages.
It is assumed that a shift register circuit is operated with 10 V and that a buffer circuit is operated with 16 V. In this case, it is necessary to convert the voltages into other values by a level-shifting circuit. Sometimes, a shift register circuit may be constructed by combining a counter circuit with a decoder circuit. A vertical scanning driver circuit 305 for transmitting gate signals to gate lines comprises a shift register circuit, a level-shifting circuit, and a buffer circuit.
It is expected that a control circuit 306 will be located in the position shown in FIG. 3 in near future. Since the control circuit 306 is composed of complex logic circuitry or memory circuitry such as a processor occupying a large area, it is expected that the total area occupied will increase.
As described above, the pixel matrix circuit 302, the horizontal scanning driver circuit 304, the vertical scanning driver circuit 305, and the control circuit 306 are generally disposed on one glass substrate 301. Accordingly, in order to secure a maximum display area on a given size of glass, it is necessary to minimize the area occupied by circuits other than the pixel matrix circuit.
However, even if the marginal structure as shown in FIG. 3 is adopted, limitations are imposed on increases of the device density of the peripheral driver circuits. Where other values or advantages are added like a control circuit, it is more difficult to increase the area of the pixel matrix circuit.